Crude Oil

You collect crude oil to turn it into fuel. Smash the oil barrels along the roads on a loot run and it piles up next to the low grade fuel they also drop, but until it goes through a refinery it is dead weight in your pockets.

So the refinery comes first. Once you have one, the loop is simple:

Barrels keep a small group going. If a pump jack turns up in a crate, place it on an oil crater you found with a survey charge and the supply stops being your problem. Guard it, though. A pump jack running all night is the kind of thing a neighbour notices.